Prior art interactive buffered raster displays include low-persistence phosphor multiple gun color cathode ray tubes (CRT's). Such a CRT is the electronic medium upon which an image is painted by way of electron beam deflection and intensity modulation of its multiple colored guns. Information, both defining the image to be painted and providing the necessary control, is obtained from a buffer intermediate the CRT display and a stored program-controlled processor. The processor executes lists of graphical orders ultimately resulting in the CRT painted image. In executing its tasks, the processor causes bit values in the form of a multibit code to be stored in a counterpart location in the buffer. The multibit code, termed a "pel", consists of an x,y position coordinate and a color number or value. As each pel is extracted from the display buffer during a horizontal scan of a raster-driven display, the bits are used to index a translate table which converts them into a larger number of bits. This larger number of bits, in turn, drives designated red, green, and blue digital-to-analog converters actually modulating the multigun CRT beam intensities.
Foley and Van Dam, "Fundamentals of Interactive Computer Graphics", Addison-Wesley Publishing Co., 1982, devote chapter 12 (pp. 479-503) to the rudiments of a raster display architecture. Also, at pp. 456-460, they describe the contemporary state of the art in the ascertaining of the boundary of arbitrarily-shaped closed polygons and the filling thereof for a bit-mapped presentation/display system such as an interactive stored processor control raster color-coded display. The preferred method described on pp. 457-458 for ascertaining the shape of the polygon to be filled involves finding the intersections of a scan line with all the edges of a polygon, sorting the intersections by an increasing x coordinate, and filling in all pels between pairs of intersections.
Agui et al, U.S. Pat. No. 4,334,274, "Method of Determining Whether or Not a Region in a Picture is Within a Closed Boundary, and an Apparatus Therefor", issued June 8, 1982, describe a method for resolving ambiguous pels or pixels bordering a black/white object by edge-detecting the object and overlaying said edge with logical positive and negative object images. This permits ascertaining ambiguous pels. Thereafter, there is involved the step of either shrinking or expanding the black or white fill in the region of any ambiguous pel in order to conform to the detected object edge.
Appel and Evangelisti, "Automatic Filling of Bounded Areas in a Raster Display", IBM Technical Disclosure Bulletin, Vol. 21, pp. 1300-1303, August 1978, show the scanning and filling of a raster object starting at an arbitrary point within the object domain and then determining pel color and filling on the fly. Appel's method of filling the pel (cell) positions constituting the polygon interior requires that a cell of arbitrary color, termed a "seed" cell, be placed within the polygon. If an empty cell is adjacent (contiguous) only to the seed cell, then said empty cell is filled. The "filled" cell in turn becomes a new "seed". If an empty cell is between a cell defining the polygon border and a "seed" cell, it is left empty. Admittedly, such a recursive procedure uses no boundary equations. However, the "identify and fill" cells on the fly appear valid only for runs of simple patterns such as black objects in white fields. Indeed, where a pattern is complex such as an rXq subarray of pels of multiple colors, then the recursion becomes effectively non-terminating because where the replacement color-coded pattern corresponds at any point to the original color-coded pattern, then Appel's system of marking previously visited locations has the effect of leaving those locations unmarked.